1. Field of Invention
The present invention relates to a low maintenance high pressure viscometer configured for the study of a cement of the inorganic, organic or mixed type.
2. Description of Prior Art
Drilling oil and geothermal wells requires the use of well cements. In wells, particularly petroleum wells, it is necessary to inject a liquid cement between a metal casing and the ground formation bordering the borehole. The setting of the liquid cement isolates the various layers of the ground formation around the borehole and holds the casing in place. For successful cementing it is important to use a liquid cement having a clearly determined rheological profile in order to determine true “pumpability time” (or setting time). Too short a time would result in premature clogging, and too long a time would needlessly delay resumption of work after cementing. Thus, for development and testing of well cements, pressure vessels are required to simulate downhole conditions accurately and repeatably. A rheometer configuration to enable cement testing of this kind makes it possible to follow the rheological changes over time of a progressively hardening material under conditions very close to the real conditions likely to be encountered downhole.
However, when testing cement samples, standard rheometer hardware (such as that as shown in U.S. Pat. No. 7,412,877) is prone to undesirably long test setup times, as well as extended cleanup and maintenance times, and can even become damaged when testing fluids such as cements as the cement sets or becomes solid. U.S. Pat. No. 4,653,313 describes a container for testing cement sample under pressure. However, this configuration would not provide sensitive and accurate measurement because of the friction between the central shaft and the seal around it. As a matter of fact, any seal directly in contact with the moving torque measurement parts would cause a considerable number of measurement errors due to friction.
Therefore, it is an object of this invention to provide a viscometer configuration allowing the rheological testing of cements under conditions closely simulating downhole conditions while avoiding contamination of cement samples with pressurization fluid.
It is another object of this invention to provide a viscometer configuration that requires substantially less maintenance work than would normally be necessary when testing cements, yet meets industry standards of accuracy, reliability, durability, dependability, repeatability, and ease of cleaning.